JAVA笔记3__字符串String类/对象一对一关联

import java.lang.String;
import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        //方式一：会创建两个字符串对象（会在字符串常量池中也存一份）
        String a = new String("dining1");
        //【尽量使用这种方式】方式二：最多创建一个字符串对象。（在字符串常量池中找有没有，有则直接指过去,否则创建，然后指过去。）
        String a1 = "dining2";
        System.out.println(a+" "+a1);
        
        //case 1:
        String b = "b1";
        String b1 = "b"+1;
        System.out.println(b==b1); //b和b1在编译期间就已确定，都指向常量池的同一块地方
        
        //case 2:
        String c = "c1";
        int t1 = 1;
        String c1 = "c"+t1;
        System.out.println(c==c1); //c1在运行期才确定
        
        //case 3:
        String d = "d1";
        final int t2 = 1;
        String d1 = "d"+t2;
        System.out.println(d==d1); //t2在编译期就已确定 
        
        //case 4:
        String e = "e1";
        final int t3 = getE();
        String e1 = "e"+t3;
        System.out.println(e==e1); //t3在运行期才确定 
    }
    public static int getE(){
        return 1;
    }
}

 

import java.lang.String;
import java.util.Scanner;

public class Main {
    //更多String类的属性和方法查Java手册
    public static void main(String[] args) {
        String s = "abcdefg";
        char c = s.charAt(s.length()-1);
        System.out.println(c);
        
        //把字符串转换成字符数组
        char [] cs = s.toCharArray();
        System.out.println(cs.length);
        for(int i=0;i<cs.length;++i) System.out.print(cs[i]+" "); System.out.println();
        
        byte[] bytes = s.getBytes(); //字节数组
        System.out.println(bytes.length);
        for(int i=0;i<bytes.length;++i) System.out.print(bytes[i]+" "); System.out.println();
        
        String ss = "我是一棵白菜";
        String ke1 = ss.substring(1,3); //[1,3)
        System.out.println(ke1);
        
        //.......
    }
}

 

/**
 * 对象的一对一关系 
 */
public class Main {
    public static void main(String[] args) {
        Husband h = new Husband("fish7");
        Wife w = new Wife("dining");
        h.wife = w;
        w.husband = h;
        System.out.println("I'm "+h.name+". My wife is "+h.wife.name);
        System.out.println("I'm "+w.name+". My husband is "+w.husband.name);
    }
}

class Husband{
    String name;
    Wife wife; //关联妻子类
    public Husband(){};
    public Husband(String name) { this.name = name; }
}
class Wife{
    String name;
    Husband husband; //关联丈夫类
    public Wife(){};
    public Wife(String name) { this.name = name; }
}